[lustre-discuss] backup zfs MDT or migrate from ZFS back to ldiskfs

[Isaac Huang]

On Fri, Jul 21, 2017 at 12:54:15PM +0800, Stu Midgley wrote:
> Afternoon
> 
> I have an MDS running on spinning media and wish to migrate it to SSD's.
> 
>     Lustre 2.9.52
>     ZFS 0.7.0-rc3

This may not be a stable combination - I don't think Lustre officially
supports 0.7.0-rc yet. Plus, there's a recent Lustre osd-zfs bug and
its fix hasn't been back ported to 2.9 yet (to the best of my knowledge):
https://jira.hpdd.intel.com/browse/LU-9305

> How do I do it?

Depends on how you've configured the MDT pool. If the disks are
mirrored or just plan disks without any redundancy (i.e. not RAIDz),
you can simply attach the SSDs to the hard drives to form or extend
mirrors and then detach the hard drives - see zpool attach/detach.

-Isaac